Radio tuning device



pr 2l., 1936.. A A, THQMAS 2,038,321 Y l RADIO TUNING DEVICE Original Filed July 23, 1929 ,-0 INVENTOR Patented Apr. 21, 1936 PATENT OFFICE RADIO TUNING DEVICE Adolph A. Thomas, New York, N. Y., assignor to Radio Corporation of America, New York, N. Y., a corporation of Delaware Application July 23, 1929, Serial No. 380,423

Renewed December 31, 1935 3 Claims.

My invention relates to radio receivers, and its object is to provide means for tuning in any station without operating the loudspeaker until the desired station is in. This eliminates unnecessary noise and permits silent tuning.

When the dial of a radio set is operated to get a particular station, the loudspeaker gives out a sound every time a tuning position is reached for any station on the air. These unwanted sounds are frequently disagreeable roars, especially if the dial is turned fast and the volume control in loud position.

This objectionable feature is overcomeby the use of my invention, which comprises the idea of switch connections controlled by the tuning knob or other nger piece. In a simple embodiment of the invention, the tuning knob is mounted on a rotary shaft adapted to be moved axially for opening and closing a switch in the loudspeaker circuit, or in any other circuit of the receiver. Thus, when the knob is pulled out, the loudspeaker is disconnected and the knob may be turned either way to bring the indicator into any position. When the station wanted is in tune, the knob is slightly pushed in, or (in one form of the invention) is lsimply released and a spring automatically closes the loudspeaker circuit The novel features and practical advantages of my tuning device will be understood from a description of the accompanying drawing, in which- Fig. 1 shows one embodiment of my invention, partly in vertical section, the axially movable shaft of the tuning knob being in circuit-closing position;

Fig. 2 is a portion of Fig. 1 with the tuning knob pulled out to open the associated switch;

Fig. 3 is a simplified circuit diagram for the switch controlled by the tuning knob;

Fig. 4 represents a modification in which the shaft of the tuning knob is normally held rearward in circuit-closing position by a spring;

Fig. 5 is a portion of Fig. 4, to show the switch open when the knob is pulled out; and

Fig. 6 is a fragmentary structural detail, partly sectioned, of the inner end ofthe knob shaft.

Referring to Figs. 1 and 2, the tuning shaft I0 operating one or more condensers C is rotatably supported in the radiol cabinet in any practical way. The front end of shaft I0 is journalled in a bearing I2 carried by a post or standard I3 which forms Vpart of a frame or bracket I4 secured to the bottom I5 of the radio cabinet. A gear I6 fixed on tuning shaft I0 carries (or other- (Cl. Z50-20) wise operates) an indicating dial I1 visible through a sight opening I8 in the front panel I9 of the cabinet. 'Ihe supporting bracket I4 is provided with a pair of aligned bearings and 2l for supporting a shaft 22, which projects through 5 the front panel on the receiver and carries a knob 23 or other suitable finger piece. A pinion 24 fixed on shaft 22 is permanently in mesh with the gear I6 on tuning shaft I0. The transmission ratio between gear members I6 and 24 is such that 10 the tuning shaft II is operated with sufficient slowness for tuning in any station when the knob 23 is turned in the usual way. The operating shaft 22 is supported not only for rotation, but also for axial or slidable movement. By grasping the knob 23, the operator can pull the shaft 22 out until the hub 24' of pinion 24 strikes the rear face 2l of bearing 2l. The inward movement of shaft 22 is limited by the rear face of pinion 24 striking the front face 20 of bearing 20.

The bearing bracket I4 carries an insulated block 25, which may be attached by screws 26 to an upstanding lug 21 of the bracket. The block may be molded of bakelite or similar material. Two insulated switch arms 28 are secured 25 to one end to block 25 by screws 29, which may also be used as binding posts for conductors 30 and 3l. If block 25 is of metal, separate insulation is required for the switch arms, which are preferably in the form of spring blades formed 30 at their free ends with lateral offsets or cams 32. The rear end of operating shaft 22 is in the form of a cone-shaped knob or extension 33 arranged to project between the free ends of spring blades 28. A ring 34 of brass or other good conducting 35 metal is mounted on shaft 22 so as to be engaged by switch arms 28 when the shaft is pushed in, as shown in Fig. 1. This closes the circuit in which the switch arms 28 are connected. When the shaft 22 is pulled out, as shown in Fig. 2, the cone-shaped end piece 33 separates the switch arms and holds them in open position. The shape of member 33 is such that the lateral offsets 32 of switch arms 28 exert sufficient pres# sure to hold shaft 22 firmly in either of its opera- 45 tive positions. A simple way to attach vthe switch-operating member V33 to shaft 22 is by means of a screw-plug or extension 35 on member 33, as clearly shown in Fig. 6. The parts 50 33 and 35 may be molded in one piece, as of bakelite, porcelain, and the like. The connecting ring 34 may be mounted on the neck portion 36 of member 33, so that the ring is automatically fixed in place when member 33 is screwed on 55 shaft 22. 'Ihe latter may be of metal or of insulating material, such as bakelite.

Fig. 3 illustrates a simplified circuit diagram to show how the switch 28 controls the driving unit 31 of a loudspeaker diaphragm 38. In this instance, the talking circuit of driving unit 31 includes the secondary coil 39 of an output transformer 40, which is supposed to be properly connected to the radio receiver. When the operating shaft 22 is pulled out, as shown in Fig. 2, the knob 23 may be rotated to actuate the tuning shaft I while the loudspeaker circuit remains open. When the indicating dial is in proper position for the desired station, the knob 23 is pushed in to close the switch arms 28 through contact ring 34. The loudspeaker circuit is now closed and the receiver operates in the usual way.

In the modification of Fig. 4, the operating shaft 22 is normally held rearward by a tensioned coil spring 4| arranged between the bearing 2| and pinion 24. If desired, washers 42 of hard metal may be interposed to take up the friction wear at the ends of the spring. The rearward axial movement of shaft 22 is limited by the engagement of pinion 24 with bearing 20. A flange 43 at the rear end of shaft 22 strikes the rear face of bearing 20 when the shaft is pulled out as shown in Fig. 5. An insulating tip 44 screwed into the rear end of shaft 22 controls a pair of switch arms 45 and 46 mounted in a suitable insulating support 41, which may consist of blocks held together by a screw or bolt 48. A screw 49 secures the blocks 4l to an extension 50 of the supporting frame I4. The switch arms 45 and 46 are preferably flexible spring blades adapted to be forced into firm pressure contact when the shaft 22 is held in normal rearward position by the tensioned coil spring 4|, whereby the loudspeaker circuit is closed. When the knob 23 is pulled out, the switch arms 45 and 46 automatically spring into open position. In other words, if a person wants to rotate the tuning knob 23 without operating the loudspeaker every time a station is passed on the dial, he simply holds the knob pulled out until the desired station is in tune. When the knob 23 is released, the spring 4| automatically moves the shaft 22 into normal circuit-closing position, as shown in Fig. 4.

It will thus be seen that I have provided an exceedingly simple arrangement to permit silent tuning of a radio set by manipulating nothing else than the tuning knob. The rotary movements of this knob actuate the tuning shaft, while the axial movements thereof control the loudspeaker circuit. In the broader aspect of this invention, the switch arms 28 and 45-46 may control any circuit of the radio receiver to prevent operation of the loudspeaker until the switch is closed. It is immaterial whether the circuit-closing position of shaft 22 is its rearward or its forward position.

An important practical feature of my invention is the fact that it also permits tuning in the regular way,namely, with the loudspeaker going. This loud tuning is necessary in those frequent cases where a person turns the knob not to get a particular station but to find a broadcast program that will suit him. Manifestly, during this fishing expedition (as I may call it) the loudspeaker must be in operative condition, so that each station may be heard as it crosses the tuning point. In the illustrative embodiments of Figs. 1 and 4, the knob 23 is pushed in for loud tuning. For silent tuning, it is pulled out a small fraction of an inch. In Fig. 4 the lmob is automatically held in loud tuning position by spring 4|, so that silent tuning is accomplished by turning the knob while it is pulled out. So little force is required to keep the knob pulled out that a child can do it without effort. When I speak. of the loudspeaker circuit being closed or opened, I mean that its condition is rendered operative or inoperative. When switch 28 or 45-46 is in series with the driving unit 3l, the loudspeaker is operative when either of these switches is closed. Manifestly, however, the switch controlled by knob 23 may be in a shortcircuit connection shunted across the terminals of coil 39. In that case, the loudspeaker is operative when switch 28 or 45-46 is open, and vice versa. It will therefore be understood that when in the claims I refer to the closing and opening of the loudspeaker circuit, I mean its operative and inoperative condition.

Although I have shown and described certain specic constructions, I want it understood that my invention is not limited to the details set forth. It is manifest that the basic principle of my invention may be mechanically embodied in other ways without departing from the scope of the appended claims.

I claim as my invention:

1. In a radio receiver, a rotary spindle carrying a finger piece at its outer end, a tuning shaft actuated by the rotary movements of said spindle, means for mounting said spindle for axial movement, a cam-shaped insulating projection attached to the inner end of said spindle, a pair of resilient switch arms supported adjacent said projection which is arranged to extend between said arms, and contact means on the inner end of said spindle for electrically connecting said switch armswhen the spindle is pushed in, said insulating cam projection holding the switch arms open when the spindle is pulled out, said pair of resilient switch arms cooperating with said cam projection to hold the spindle in either of its axial positions 2. In a radio receiver, a rotary spindle carrying a nger piece at its outer end, a tuning shaft actuated by the rotary movements of said spindle, means for mounting said spindle for axial movement, a cam-shaped insulating projection attached to the inner end of said spindle, a pair of spaced resilient conducting members supported adjacent said projection which is arranged to extend between said members, and contact means on the inner end of said spindle for electrically connecting said conducting members when the spindle is pushed in, said insulating cam projection holding the conducting members open when the spindle is pulled out, said pair of resilient conducting members cooperating with said cam projection to hold the spindle in either of its axial positions.

3. The invention defined in the preceding claim wherein the spaced resilient conducting members are connected to the radio receiver loudspeaker circuit whereby during the tuning operation by the rotary spindle the energization and deenergization of said loudspeaker circuit are also controlled by said rotary spindle.

ADOLPI-I A. THOMAS. 

